harbour-containers VS ubuntu-touch

You can run a desktop with https://github.com/sailfish-containers/harbour-containers

Have you checked out harbour-containers?

Ubuntu Touch, for example, does not support Full Disk Encryption, when Android has moved on from Full Disk Encryption to File-Based Encryption. Android utilises SELinux in enforcing mode for Mandatory Access Control even for root/superuser processes. Sandboxing with Flatpak cannot compare to the OS-level app sandboxing done on Android and iOS. Permission management on Flatpak is good, but still not as advanced as Android or iOS. On phones, (real) Linux is quite easily outclassed in security when compared to Android.

For those seeking a change https://ubports.com/

It still uses many of the Android components via Halium on traditional Android devices which end up unpatched and for devices not with a mainline kernel use outdated vendor kernels. https://github.com/ubports/ubuntu-touch/issues/1566

I'd suggest taking a look at contributing to existing efforts like UBPorts

Ubuntu Touch doesn't even have encryption and ships kernels with many known security issues: https://github.com/ubports/ubuntu-touch/issues/178

Fyi, the project isn't dead, it is just not developed by Canonical anymore: https://ubports.com/

There is already Ubport https://ubports.com/ project that is supporting Ubuntu for smartphones and guides you to compile debian with all the phone functionalities. Some parts of modem abstraction layer on the Linux (below radio Interface layer) will still be not openesource and i would say it won't be easy to get this source.